The development over the past decade of methods for delivering genes to mammalian cells has stimulated great interest in the possibility of treating human disease by gene-based therapies. Gene transfer technology has advanced considerably over the past few years. Both ex vivo and in vivo gene transfers into a variety of cells and organ systems have been accomplished. In the ex vivo form of gene delivery, cells derived either from the patient or from other sources, are first generally modified outside of the body by introduction of a particular gene or genes. These cells are then re-introduced into the body, so as to achieve either local, regional or widespread distribution. In the in vivo form of gene delivery, the gene is carried in an appropriate vehicle such as a viral vector or is introduced by non-viral means such as by lipofection or direct injection into the body. The advances of in vivo gene therapy are its relative cost advantage as well as the fact that the gene can be treated as a drug.
While retroviral vectors are used primarily in ex vivo gene therapy, adenovirus based vectors are vectors of choice for in vivo gene transfer. The advantages of adenovirus therapy include: (i) ability to transfer genes with very high efficiency into many cell types without the need for cell replication; (ii) high titers of the virus are easily achievable; (iii) they can accept large DNA fragments up to approximately 8 kb; and (iv) adenoviruses are considered to be relatively safe, because most adults have in fact acquired immunity against a variety of adenoviruses and adenovirus-attenuated vaccines have been safely used in man. However, one of the major limitations is that the expression of the adenovirus is transient, lasting from several weeks to several months. This is due to the fact that DNA introduced into a cell by an adenovirus based vectors will not incorporate into the host genome. Moreover, immune response from the host can eliminate adenovirally infected cells. New generation of adenoviruses are expected to overcome the latter problem.
In spite of the major advances in the field of gene-therapy, gene transfer into the mammalian kidney has proved difficult because of the structurally complex organization of the organ and its relatively low mitotic index. Moreover, the architectural organization of the kidney is critical for proper organ function. Thus, high efficiency gene delivery to one particular cell type may be difficult to achieve. Very little literature exists on the in vivo delivery of genes into the kidney.
Tomita et al. (Biochem. and Biophys. Res. Comm. 186:129-134, 1992) report a method for in vivo gene transfer into the rat kidney. They utilize HVJ (Sendai virus) and liposome methodology. In this protocol, plasmid DNA and a nuclear protein are coencapsulated in liposomes and later cointroduced into cells. The reporter gene utilized in these studies was the SV40 large T antigen. The gene transfer was conducted by inserting a catheter proximal to the right renal artery with the abdominal aorta clipped distally beneath the left renal artery. The liposome suspension was injected into the kidneys. Four days after the injection of this mixture, SV40 large T antigen was detected immunohistochemically in 15% of glomerular capillary cells. The expression of the T antigen declined rapidly over the ensuing 2-3 days. Interestingly, no expression of the foreign gene was detected outside of the glomerulus. Akami et al. (Transplantation Proceedings 26(3):1315-1317, 1994) have used a similar HVJ-liposome complex to introduce human CD59 gene into canine kidney in vivo. They report transient and insufficient expression of the CD59 gene in the glomerular cells of the kidney.
A study by Zhu et al. (Science 261:209-11, 1993), reports the use of a particular cationic liposomc DNA mixture to deliver genes with high efficiency into a vast number of endothelial cells in a rat. The gene transfer protocol is initiated by tail vein injection. The study reports long-term expression in almost all of the endothelial cells of the body as well as in a variety of parenchymal cell types including the lung, spleen, lymph nodes, and bone marrow. It also reports that between 25-50% of endothelial cells in the kidney are transfected, but does not provide any information on whether these endothelial cells are in glomerular or non-glomerular regions. Also, there is no indication of the duration of expression in these kidney cells.
Moullier et al. (Kidney International 45:1220-1225, 1994) provides a first report of an adenoviral-mediated gene transfer into a kidney in vivo. A replication deficient adenoviral vector that contained a .beta.-gal reporter gene was selectively perfused into the renal artery or infused through a retrograde catheter into the pyelic cavity of the adult rat kidney. Transient (2-4 weeks), low levels of the .beta.-gal expression were observed in the proximal tubular cells, when the adenoviral vector was selectively perfused via the renal artery, while expression was observed in tubular cells from the papilla and medulla when the adenoviral vector was administered by retrograde infusion. No expression was observed in the endothelial cells of the kidney.
Therefore, the need still exists for development of methods for a more efficient in vivo gene transfer into specific kidney cells.